Coin receptacles (e.g. coin tubes) can be used to store coins in a currency handling apparatus. Various techniques can be used to measure the available capacity for a coin tube to store additional coins.
For example, in some implementations, a processor can compute the available capacity of a coin tube by comparing a running count of the quantity of coins inserted into the coin tube against a predetermined quantity of coins that the receptacle is known to be capable of storing. The processor can use the computed available capacity to determine whether to stop accepting coins of a particular denomination and/or whether servicing is required.
This approach is predicated on an assumption that the stored coins have a fixed dimension (e.g. thickness). Such an assumption can result an inaccurate computation of the available capacity because the coin dimensions can vary for various reasons (e.g. manufacturing tolerances, environmental conditions, etc.). Inaccurately computing the available capacity can result in underfill or overfill of the receptacle. Overfilling or underfilling of the receptacle can lead to jams and/or downtime of the currency handling apparatus.
This approach also relies on an assumption that the coins will always be received and stored in a pre-determined orientation (e.g. stacked face-to-face). To the extent that the coins are not received and stacked in the pre-determined orientation, it is possible for the coin tube to reach or exceed maximum capacity prior to receiving the predetermined quantity of coins. For example, coins or foreign objects lodged within the coin tube can prevent subsequently inserted coins from being stacked in the pre-determined orientation, which can potentially cause the coin receptacle to reach or exceed the maximum capacity prior to receiving the predetermined quantity of coins. In this situation, the processor may not detect the overflow event, resulting in overflow of the coin tube and malfunction of the currency handling apparatus.
Ultrasonic pulses can also be used to measure the available capacity of a coin receptacle. In some implementations, ultrasonic pulses can be directed towards the top of a coin stack, and the time delay between the emitted and reflected pulses can be measured. However, ultrasonic transducers are resonant structures that produce ringing, and are therefore difficult to construct. Moreover, while damping can be used to reduce the ringing, such damping also has the negative effect of reducing the output power and can lead to potential noise problems. Also, it may be necessary to space such an ultrasonic transducer a large distance from the stack of coins to avoid detection of the reflected pulse occurring prior to a complete detection of the emitted pulse. Furthermore, if a substantial portion of the transducer output is coupled to the surrounding structure, this can result in saturation of the receiving microphone.
Therefore, there exists a need for a more efficient, smaller form-factor, high-accuracy capacity detector that can determine the available capacity of a coin tube.